Image display systems based on spatial light modulators (SLMs) are an alternative to image display systems based on cathode ray tubes (CRTs). SLM systems provide high resolution without the bulk of CRT systems.
Digital micro-mirror devices (DMDs) are one type of SLM, and may be used for either direct view or for projection displays. A DMD has an array of hundreds or thousands of tiny tilting mirrors, each of which provides light for one pixel of an image. To permit the mirrors to tilt, each mirror is attached to one or more hinges mounted on support posts, and spaced by means of a fluidic (air or liquid) gap over underlying control circuitry. The control circuitry provides electrostatic forces, which cause each mirror to selectively tilt. For display applications, image data is loaded to memory cells of the DMD and in accordance with this data, mirrors are tilted so as to either reflect light to, or deflect light from, the entrance pupil of a projection lens and then to an image plane.
One approach to providing color images in an SLM display system is referred to as "sequential color". All pixels of a frame of the image are sequentially addressed with different colors. For example, each pixel might have a red, a green, and a blue value. Then, during each frame period, the pixels of that frame are addressed with their red, green, then blue data, alternatingly. For this type of system, one type of sequential color filter is a color wheel having three segments of these same colors is synchronized to the data so that as the data for each color is displayed by the SLM, the light incident on the SLM is filtered by the color wheel. Another type of sequential color filter is a liquid crystal color modulator, which has a stack of liquid crystal and polarizing layers. These layers are conFIGUREd and controlled so that only one color passes at a given time. For standard display rates, such as the 30 frame per second NTSC rate, the eye perceives the image as having the proper color.
A problem with existing sequential color filters, such as color wheels and liquid crystal color filters, is that they provide color at the expense of brightness. To generate a saturated primary color such as red, green, or blue, two-thirds of the total useable light from a white light source is wasted.